Car that needs refueling only every 100 years

An engine being developed in the US could result in cars that run for 100 years on just a single fuel fill-up. Connecticut-based Laser Power Systems is building the turbine engine and electric generator tied to a laser using thorium - a naturally-occurring mildly radioactive element that is one of the densest materials on the planet.

The density means it's highly efficient in producing huge amounts of heat. One gram of the thorium delivers more energy than 28,000 litres of petrol, and about eight grams could power the car's engine for 100 years.

And the research and development isn't just aimed at resulting in some sort of sci-fi one-off concept car. Laser Power Systems intends to put the engine into mass-production, and sees a future in which the thorium turbine could power a huge number of the one billion cars on the world's roads -- massively reducing emissions.

The latest version of the engine weighs around 250kg -- about the weight of an old-school iron block V8 -- and is small enough to fit under the bonnet of most cars.

This isn't the first time thorium has been touted as a car fuel, with the Cadillac World Thorium Fuel concept -- or Cadillac WTF, as it quickly became known -- unveiled by General Motors at the 2009 Detroit motor show to promote Caddy's centenary.

To celebrate the landmark, the WTF also boasted a 100-year refill span and the same period of time maintenance-free on all its systems, although the 'tyres' (actually six integrated wheels at each corner) were said to need adjustment every five years or so. However the claims were theoretical, and the concept never reached the working prototype stage.

Laser Power Systems wants to take the technology to the production line, and already sounds optimistic, with their website enthusiastically promising the prospect of unlimited emissions-free power, a new era in sustainable green technologies -- and even revitalisation of the US economy. You can probably take some of that with a grain of salt, but it sounds like a grain of thorium might just take you further.